1. Field of the Invention
The present invention relates to a lubricant applying device usable in electrophotography apparatuses such as copiers, printers, and facsimiles, a process cartridge configured to be replaced together with the lubricant applying device in a lump, and an image forming apparatus including them.
2. Description of the Related Art
An image forming unit of an electrophotography apparatus such as a copier needs to be equipped with a cleaning device for removing toner that is not transferred onto a transfer sheet but remains in a transfer process, or adherent substances that are present, on a photoreceptor or an image carrier called an intermediate transfer element. In general, a cleaning blade formed of an elastic body such as rubber is used as a cleaning means of the cleaning device and is in contact with the image carrier in the counter direction against the movement of the image carrier.
In addition, further provided is a mechanism that applies a lubricant such as zinc stearate onto the surface of the image carrier in order to maintain the surface friction coefficient of the image carrier at a desired value, thereby preventing an additive of the toner from sticking to the image carrier, or preventing the toner from being incompletely transferred onto the image carrier, which brings about toner residue on the image carrier, due to an increase in friction in the transfer process.
The lubricant applying mechanism scrapes a lubricant off a lubricant bar, which is in press-contact with the applying mechanism, with the use of a brush roller and adheres the lubricant attached to the brush roller onto the image carrier in the downstream of the transfer process. The lubricant attached to the image carrier is spread thin with the use of a cleaning blade which is in contact with the image carrier in the counter arranged in the further downstream side thereof, against the movement of the image carrier.
However, in regard with the application amount of lubricant applied onto the image carrier, an appropriate amount varies depending on the amount of toner developed on the image carrier. Therefore, for example, Japanese Patent Application Laid-open No. 2002-244485 discloses an image forming apparatus which includes a lubricant film-forming means and an image data counting means. The lubricant film-forming means attaches a solid lubricant to a rotating brush and applies the lubricant attached to the brush onto an image carrier, so that a film of the lubricant is formed on the surface of the image carrier. The image data counting means counts image formation information that is used to form an image on the image carrier. In the image forming apparatus, the amount of the lubricant to be applied onto the surface of the image carrier is controlled on the basis of the information from the image data counting means.
Further, Japanese Patent Application Laid-open No. 2009-008818 discloses a lubricant applying device including a holder and a rotating member. The holder holds a solid lubricant therein. The rotating member scrapes a lubricant off the solid lubricant held by the holder and applies it onto an image carrier. The lubricant applying device further includes a rotation speed control device that changes the rotation speed of the rotating member while images are being formed on the image carrier.
Furthermore, Japanese Patent Application Laid-open No. 2009-008819 discloses a lubricant applying device including a molded-lubricant holder that holds a molded-lubricant and applies the lubricant supplied from the molded-lubricant onto the surface of an image carrier. In the lubricant applying device, the molded-lubricant holder is configured to be replenished with a new molded-lubricant when the molded lubricant is consumed and thus becomes small.
Moreover, Japanese Patent Application Laid-open No. 2005-070276 discloses an image forming apparatus which includes an image carrier; a charging mechanism; an exposing mechanism; an developing mechanism and a cleaning mechanism, and the image forming apparatus including a transfer mechanism and a fixing mechanism. The image carrier is configured to carry a latent image thereon. The charging mechanism uniformly charges the surface of the image carrier. The exposing mechanism performs an exposure on the basis of image data so as to write a latent image on the charged surface of the image carrier. The developing mechanism supplies a toner to the latent image formed on the surface of the image carrier so as to turn the latent image into a visible image. The cleaning mechanism cleans the surface of the image carrier. The transfer mechanism transfers the visible image on the surface of the image carrier to a recording medium directly or via a process of transferring it to an intermediate transfer element. The fixing mechanism fixes the toner image on the recording medium. The image forming apparatus further includes an applying mechanism provided between the cleaning mechanism and the charging mechanism to apply a contained lubricant onto the image carrier with an applying blade, thereby forming a thin layer.
Also, Japanese Patent Application Laid-open No. 2007-322449 discloses a lubricant applying device applying a lubricant by pressing the lubricant against the surface of a rotating body. The lubricant applying device includes a rotatable shaft; a solid lubricant; and a driving mechanism. The rotatable shaft is provided substantially parallel to a rotating shaft of the rotating body. The solid lubricant is formed to have a substantially constant layer thickness, on a predetermined portion of the outer circumference of the shaft in the circumferential direction, and of which the leading end face in the rotating direction of the shaft acts as a pressed surface against the rotating body. The driving mechanism rotates the shaft in order to press the solid lubricant against the surface of the rotating body.
However, in Japanese Patent Application Laid-open No. 2002-244485, a change in application amount requires an extensive change of the apparatus such as a change in the rotation speed of the brush, so it is difficult to reduce the sizes of a lubricant applying mechanism and the image forming apparatus. Further, in Japanese Patent Application Laid-open No. 2009-008818, in order to make the rotation speed variable, a part such as an additional driver is required. Therefore, the number of parts increases and it incurs an increase production cost. In Japanese Patent Application Laid-open No. 2009-008819, the replenishment requires time and a technique and thus the solid lubricant replenishment is difficult. In Japanese Patent Application Laid-open No. 2005-070276, since there is only a little space to accommodate the solid lubricant in the apparatus, it is difficult to use the solid lubricant over a long period of time.
In Japanese Patent Application Laid-open No. 2007-322449, use of an electromagnetic clutch may enable the change in an applied pressure according to the rotation speed of an applying member. However, the electromagnetic clutch is expensive. Further, in Japanese Patent Application Laid-open No. 2007-322449, the movement of the applying member is little. Specifically, in the related art, the consumption of a lubricant is about 2 g per 1000 sheets, the consumed speed of the lubricant is 0.7 mm per 1000 sheets (on the assumption that the density of the lubricant is 1 g/cm3 and the lubricant width is about the longitudinal width of A4 recording paper (295 mm)). Therefore, the applying member should be driven to move minutely. Since very little movement is necessary, the applying member should be discontinuously driven or a very large reduction of speed should be performed. In the case of driving the applying member discontinuously, the driving of the applying member is enabled by the driving of a photoreceptor. This leads to a fluctuation in load to the photoreceptor due to switching between the transmission and the cut-off of drive, which results in unevenness of the speed of the photoreceptor. It is problematic because unevenness of the speed may cause unevenness of a density in an image. Further, in the case of attempting to make a large reduction of speed, many gear trains or the like are necessary, and thus a large space is required for the applying mechanism.